The effects of porcine somatotropin (pST) and dietary lysine level on growth performance and carcass characteristics of finishing swine

Seventy-two finishing pigs averaging 130 lb were utilized to determine the effects of

PST and dietary lysine on growth performance and carcass characteristics. Pigs were injected daily with 4 mg PST in the extensor muscle of the neck and fed either a pelleted corn-sesame meal diet (.6% lysine, 17.7% crude protein) or diets containing .8, 1.0, 1.2, or 1.4% lysine provided by L-lysine HCl. All diets were formulated to contain at least 200% of NRC (1979) recommendations for other amino acids. Control pigs received a placebo injection and the .6% lysine diet. Increasing levels of dietary lysine resulted in increased average daily gain (ADG) and improved feed conversion (F/G; linear and quadratic, P<.01) for PST-treated pigs.

Adjusted backfat thickness (ABF) was not affected by dietary lysine; however, PST-treated pigs had less backfat (P<.05) than control pigs. Longissimus muscle area (LMA), trimmed ham, and loin weights increased as dietary lysine was increased among PST-treated pigs (linear and quadratic, P<.01). Percentage of moisture and crude protein of the longissimus muscle increased, (linear P<.05, linear and quadratic P<.05, respectively), whereas dry matter and fat content decreased (linear P<.05). Similar trends in composition were observed for

whereas plasma lysine and insulin increased (linear and quadratic, P<.OI). Plasma glucose and free fatty acid concentrations on day 28 tended to increase (quadratic P<. I0) with increasing dietary lysine level. Plasma somatotropin level was elevated 2 to 3 times in PST-treated pigs compared to control pigs, but was not affected by dietary lysine level. Our results indicate a relatively high requirement for lysine in PST-treated pigs. Growth performance and carcass traits were optimized at dietary lysine levels of 1.2 to 1.4%, which corresponds to lysine intakes of 30 to 36 g/day. These results demonstrate that PST-administration nearly doubles the lysine requirement of finishing swine.